1. Field of the Invention
This invention relates to a fiber reinforced plastic material with improved flexibility and high tensile strength for use as a strength member in optic cables.
2. Description of the Related Art
This invention relates to the construction of a strength member used in a fiber-optic cable (FOC). In the absence of metal conductors, fiber optic cables rely on a design comprising a strength member to provide sufficient protection for the fibers from longitudinal and transverse stresses either during installation or later during service. Strength members are typically made of fiber reinforced plastic (FRP), also called glass reinforced plastic (GRP).
Fiber-reinforced plastics are composite materials made of a polymer matrix reinforced with fibers. The fibers are usually glass (most popular), carbon, or aramid, while conventionally the polymer is usually an epoxy, or vinyl ester.
Using the conventional resin system, the FRP is very stiff. Typically it has a bending stiffness greater than 6×10−3  Pa m4 for a 2 millimeter (mm) diameter rod, resulting in an optical fiber cable that is very hard to bend. While the high bending stiffness is preferred in some outdoor applications (i.e., sometimes cables are needed to be “pushed” through small diameter conduits during installation), it is highly undesirable for other applications (outdoor/indoor), where a cable needs to go inside a building and make several turns before it reaches its destination. To increase the flexibility of the cable, one has to either reduce the size of the FRP (which will reduce the total tensile strength of the cable) or to change the cable design. For instance, some cable manufacturers have modified the traditional round FOC cable with a central strength member into a flat, “tape looking” cable, which uses a flat geometry (instead of circular shape) with multiple FRPs in parallel along its width. The FRPs used in the flat cable design have a relatively small diameter, but its total tensile strength is equivalent to the traditional round cable. Compared to the traditional round cable with a central strength member, the flat cable design offers higher flexibility in one axis (along the direction of its width) while maintaining the total tensile strength of the cable unchanged. However changing the cable design does cause higher complexity in manufacturing.